R. Job

Thickness Dependence of Resistivity and Optical Reflectance of ITO Films

Indium-tin-oxide (ITO) films deposited on crystalline silicon wafer and Corning glass are prepared by direct-current magnetron sputtering method at room temperature with various thicknesses. The thickness dependences of structure, resistance and optical reflectance of ITO films are characterized. The results show that when the film thickness is less than 40 nm, the resistivity and optical reflectance of the ITO film changes remarkably with thickness. The optoelectrical properties trend to stabilize when the thickness is over 55 nm. The GXRD result implies that the ITO film begins to crystallize if only the thickness is large enough.

Lower critical field, remanent magnetization and irreversibility line of ceramic (Bi,Pb)-2223-HTSC

Abstract A detailed magnetic study of the (Bi, Pb)-2223 superconductors was carried out over the temperature range 4–120 K. At temperatures below 25 K the lower critical field H c1 was drastically enhanced. This enhancement can probably be explained either by a theory based on an intrinsic proximity effect in the normal layers of the Bi-2223 unit cell or by a blocking of the flux penetration because of a surface barrier effect. An analysis of the anomalies in the irreversibility line has been undertaken in the framework of the proximity effect allowing us to obtain also plausible values for ξ 0 , λ 0 and the Fermi velocities in the superconducting and normal layers. The temperature dependence of the large remanent magnetization at 4 K with a drastic decrease above 25 K offered evidence for a strong depinning of the vortex lattice around 25 K. Below this temperature the active pinning centers have a rather small pinning energy. Above 25 K a smaller group of pinning centers with larger activation energy gives rise to a small and weakly temperature-dependent remanent magnetization. A scaling behavior of the magnetization curves was obeyed in the temperature range between 40 and 60 K in good agreement with the predictions of an extended Bean model.

Electrical properties of lithium-implanted layers on synthetic diamond

Lithium implantation (40 and 50 keV; doses of 2 × 1016 and 4 × 1016 cm−2) has been performed in several synthetic and natural diamond crystals at room temperature (RT) and 850–900 °C (high temperature (HT) implantation). In contrast with the case of the RT implantation, the HT implantation did not result in radiation-induced surface graphitization. The samples implanted at RT and 850 °C were subsequently annealed at 900 °C. Comparison of the electrical properties of the doped crystals shows the dependence of the electrical activation on the annealing temperature. Thermal emf measurements have established that the conductivity is n-type.

Substrate orientation, doping and plasma frequency dependencies of structural defect formation in hydrogen plasma treated silicon

The formation of structural defects in hydrogen plasma treated (100)- and (111)-oriented p-type Czochralski (Cz) Si and in [100]-oriented n-type Si was studied by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The samples were treated either by a 110 MHz or 13.56 MHz hydrogen plasma at 250 ◦ Cf or 60 min. The distribution of hydrogen wa ss tudied by nuclear reaction analysis. It is found that, after the hydrogen plasma treatment, the surface of Cz Si is structured and the roughness of the surface depends on the orientation and doping level of the substrate. The defect density increases for (100)-oriented wafers for the higher plasma frequency bu tf or (111)-oriented wafers it is lower, applying the same hydrogen plasma frequency. Different defect types were found: stacking faults on {111} planes, dislocations and circular shaped defects exhibiting a strong stress field. The formation of nearly free hydrogen molecules (Raman shift of about 4150 cm −1 ) was observed by Raman spectroscopy after the plasma hydrogenation. It was found that the H2 molecule concentration depends on the concentration of structural defects. The hydrogen molecules can be formed in both n- and p-type Si, unlike the case of remote plasma hydrogenation.

Hydrogen plasma-enhanced thermal donor formation in n-type oxygen-doped high-resistivity float-zone silicon

The impact of plasma hydrogenation on the subsequent formation of thermal donors at 450 °C in n-type oxygen-doped high-resistivity float-zone silicon is investigated by a combination of electrical and spectroscopic techniques. It is shown that the increase of the doping concentration can be explained by the creation of two sets of donors. The first one is the classical double oxygen thermal donors (OTDs), which are introduced with a nearly uniform concentration profile across the sample thickness, while the second type of donors is shallower and most likely hydrogen related. The latter show a pronounced concentration profile towards the surface and they form and disappear at a much faster rate than the OTDs at 450 °C.

Magnetic relaxation and flux creep in ceramic (Bi, Pb)-2223 HTSC

Abstract The magnetic relaxation of ceramic(Bi, Pb)-2223 (Tc = 107.2K) has been studied in the temperature range 305-100 K and in fields up to μ0H = 1T. The relaxation of the magnetization at temperatures up to 80 K can be well described by a logarithmic time decay due to thermal activation of vortex lines. The activation energy U0 obtained from the relaxation rate S= 1 M ( dM dln t ) in the single barrier height model exhibits a strong temperature. Both in applied fields and in the remanent state the activation energy increases with temperature (U0 = 20–50 meV at T = 4 K, U0 = 250–400 meV at T ⋟ 60 K). The distribution of pinning barriers has been evaluated and exhibits a peak at U0 ⋟ 20–30 meV in the remanent state and U0 ⋟ 15–20 meV in an applied field of μ0H = 1 T. These small values explain the rapid drop of the remanency at T ≥ 25 K, the peak in the relaxation rate at T ⋟ 10 K and the increase of Hc1 at T ≤ 25 K.

How to fabricate low-resistance metal-diamond contacts

Abstract Three types of mesa etched contact resistance test structures with Al Si , TiAu, TiWN-Au contacts are compared. The contact resistivity was calculated using transmission-line model (TLM) theory which is fully applicable to diamond. For Al Si contacts the lowest contact resistivity was obtained after annealing at 500 °C in dry nitrogen. The lowest contact resistivity for as-deposited contacts was found for TiAu. In general, the contact resistivity drops with increasing levels of B dopant and depends on the metallization scheme. The dependence of the contact resistivity on the surface concentration of B for as-deposited Al Si contacts can be fitted by a power-law indicative of spatial inhomogenous areas in the contact region leading to an additional spreading resistance component. The contact resistivity depends exponentionally on the operating temperature for as-deposited Al Si contacts but the thermal coefficient is independent of the doping level for heavily B-doped diamond films, which is typical for tunneling.

Hydrogen diffusion at moderate temperatures in p-type Czochralski silicon

In plasma-hydrogenated p-type Czochralski silicon, rapid thermal donor (TD) formation is achieved, resulting from the catalytic support of hydrogen. The n-type counter doping by TD leads to a p-n junction formation. A simple method for the indirect determination of the diffusivity of hydrogen via applying the spreading resistance probe measurements is presented. Hydrogen diffusion in silicon during both plasma hydrogenation and post-hydrogenation annealing is investigated. The impact of the hydrogenation duration, annealing temperature, and resistivity of the silicon wafers on the hydrogen diffusion is discussed. Diffusivities of hydrogen are determined in the temperature range 270–450°C. The activation energy for the hydrogen diffusion is deduced to be 1.23eV. The diffusion of hydrogen is interpreted within the framework of a trap-limited diffusion mechanism. Oxygen and hydrogen are found to be the main traps.

The influence of the amorphous silicon deposition temperature on the efficiency of the ITO/A-Si:H/C-Si heterojunction (HJ) solar cells and properties of interfaces

Some crucial limiting process steps of ITO/(n)a-Si:H/(p)c-Si solar cell manufacturing were investigated. The influence of amorphous silicon deposition temperature on the efficiency of heterojunction (HJ) solar cells as well as ITO deposition on the properties of ITO/a-Si:H/c-Si interfaces were studied. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and SIMS measurements were employed for the investigations. It was observed that the decrease in a-Si:H deposition temperature from 230 down to 100°C leads to a reduction in solar cell efficiencies to only 1%. It was found that the ITO deposition process itself can significantly modify the ITO/a-Si:H/c-Si interfaces due to the interaction of oxygen, and In and Sn atoms with silicon at the initial stage. It was concluded that this modification has a more significant impact on the quality of the HJ solar cells than on that of the a-Si:H layer.

Investigation of the emitter band gap widening of heterojunction solar cells by use of hydrogenated amorphous carbon silicon alloys

The hydrogenated amorphous carbon-silicon alloys [a-SixC1−x(n):Hy] and [a-Six(n):Hy] layers were investigated in order to prove the feasibility to widen the optical band gap in emitters of the heterojunction solar cells. The alloys were fabricated by decomposition of silane (SiH4), phosphine (PH3), methane (CH4), and hydrogen (H2), using a plasma enhanced chemical vapor deposition. Particularly, we focused on the incorporation of hydrogen and carbon within the resulting [a-SixC1−x(n):Hy] and [a-Six(n):Hy] films, which later form the emitter. The corresponding local vibrational modes of Si−Hx, C−H, and the corresponding network have been analyzed by μ-Raman spectroscopy. The addition of carbon degrades the photoelectronic properties in the emitter layer. This deterioration can be minimized by H dilution. The resulting optical band gap EG as well as the thickness of the emitter were determined by spectroscopic ellipsometry. It was confirmed that the band gap EG can be tailored by using an appropriate gas mi...